A nifty bit of research[i] out of Stanford University this week – and a great follow up on my last post, which talked about how our bodies differentiate good versus evil when it comes to gut bacteria.
Before we can have personalized probiotics, we need to figure out not only that question – how does the human body choose its microbial content – but also, what can we do to ensure a probiotic bacteria colonizes? Not every probiotic you ingest manages to live in you. They must make it past both our immune systems and the other residents of the gut. Unfortunately, even completely beneficial bacteria are often killed off in the war zone that is the intestinal microbiome, as these microorganisms battle for space and nutrients.
To address this question, Stanford scientists wondered if they could ensure survival of a beneficial species by adding to the diet a nutrient that is particularly loved by a commensal species. They isolated a specific strain of Bacteroides that can digest an ingredient, a carbohydrate called porphyran, that’s found in nori seaweed. While commonly eaten in Japan, nori is rarely eaten in the United States.
They then took 3 groups of mice, wiped out the gut flora of 2 of them and replaced their microbiomes with those of 2 healthy American human volunteers. The third group was left with their native rodent bacteria. When fed a normal mouse chow diet, the strain of bacteria was able to colonize to a “varying and limited degree.” One of the groups of mice with human bacteria rejected the strain completely. “However, when the mice were fed a porphyran-rich diet, the results were dramatically different: the bacteria engrafted robustly at similar levels in all the mice.”
To boot, the researchers were able to dictate the population size of the strain by increasing or decreasing the amount of nori fed to the animals. They were also able to take the genes that code the ability to eat nori into other Bacteroide strains, giving these the same competitive advantage. Going forward, of course, the idea is to create therapeutic probiotic strains and blends to address specific health issues.
At some point in the not-very-distant-future, we should be able to manipulate our microbiomes through simple dietary measures. Says the lead researchers, “Our growing ability to manipulate them is going to change how precision health is practiced. A physician whose patient is about to begin immunotherapy for cancer may choose to also administer a bacterial strain known to activate the immune system, for example. Conversely, a patient with an autoimmune disease may benefit from a different set of microbiota that can dial down an overactive immune response. They are just a very powerful lever to modulate our biology in health and disease.”